In recent years, Stevia rebaudiana is gaining popularity in Europe, especially in weight control and among diabetics since it has a high sweetening power without calories. More recently, its antioxidant properties have been studied with different chemical methods; all authors have agreed that stevia has antioxidant activity.

Our study aims to better examine its antioxidant properties using a relevant model to assess the antioxidant capability of stevia extracts within human cells, to determine its efficiency of protection against free radicals under physiological conditions. To this end, stevia leaf and stem samples were subjected to water extraction, chemically characterized and subsequently the antioxidant potentials were determined in vitro through the ORAC assay and in vivo in a cell-based assay (CAA). The CAA assay measures ROS levels in the presence or absence of stevia extracts using 2′,7′-dichlorofluorescein diacetate dye, a molecule that becomes a highly fluorescent probe in the presence of oxidants. In addition, purified steviol glycosides were analyzed.

Our results showed that stevia extracts decreased the intracellular oxidation in a dose-dependent manner when compared to control cells, indicating its antioxidant action within the cell. Despite, its purified steviolglycosides showed a low ORAC value compared with crude extracts and do not elicit any cellular antioxidant activity. This study provides evidence that stevia is certainly a potential source of antioxidative agents for the food and dietary supplements companies, that apart its natural sweetness has a cellular antioxidant potential. Moreover, the antioxidant capacity both in vitro as well as in the cell-based assay is higher for crude leaves extracts than for purified steviol glycosides, thus suggesting that the polyphenols present in the crude extracts are responsible for the antioxidant activity of stevia. Thus, stevia leaves or crude extracts thereof might be considered as a food ingredient.